The long term goal of our studies is to elucidate the mechanisms whereby polypeptide growth factors regulate the development of oligodendrocytes, the myelin forming cell of the CNS. These issues are important in order for us to understand the mechanism underlying neurological disorders affecting CNS myelin. These issues are also important for devising strategies for intervention or preventative treatments in these disorders, including the promotion of regeneration by administrating agents to encourage endogenous repair processes, or transplanting cells to supplement this repair. The specific focus of this proposal is to analyze the functionally important domains of the Platelet Derived Growth Factor alpha-receptor (PDGFR alpha) that modulate the biological responses of oligodendrocytes to PDGF. The purpose of these experiments is to determine how oligodendrocytes generate diverse biological responses from a single growth factor. PDGF is one of at least seven ligands acting via receptors with tyrosine kinase activity that affect oligodendrocyte development, and has a diverse range of biological effects including the ability to modulate progenitor cell proliferation, migration, differentiation and survival. The fundamental question addressed in this proposal is whether specific domains of PDGFR alpha, associated with distinct intracellular second messenger signaling pathways, are linked to separate biological responses of oligodendrocyte progenitors to PDGF. This hypothesis will be addressed using a combination of in vitro and in vivo approaches. First, mammalian cell expression vectors encoding mutant versions of PDGFR alpha will be transfected into primary oligodendrocyte progenitors, and clonally selected cells will be examined for PDGFR alpha transgene-mediated biological responses in vivo. The PDGFR alpha transgenes will be engineered such that they can be specifically activated by a neutral ligand (hCSF-1), and will include mutations in domains of PDGFR alpha predicted to block activation of individual second messenger pathways. Second, mutated PDGFR alpha cDNAs will be introduced into progenitor cells isolated from PDGFR alpha-null (Patch) mice, and the effects of specific mutations on oligodendrocyte development will be analyzed after transplantation in vivo. The results of these experiments should (1) identify intracellular domains of PDGFR alpha and the signal transduction pathways associated with these domains regulating the proliferation, migration, differentiation and survival of oligodendrocyte progenitors; and (2) determine whether individual domains are associated with these specific biological responses, in vitro and in vivo.